The present invention relates to storage tanks which may be used to store liquid or semi-liquid substances. Although a tank constructed according to the principles of the invention may be utilized for storing a wide variety of materials, it is particularly adaptable for use as a farm manure bank. As the price of artificial fertilizers rises, it has become increasingly advantageous for farmers to store manure for subsequent soil fertilization. A number of storage tank structures have been available for use as manuare banks; however, they have been found to be unsatisfactory for a variety of reasons, such as necessitating expensive equipment and/or skilled labor for construction; unsafe in seismically active locations; inability to enlarge the capacity of the tank or relocate the tank; susceptable to corrosion failure.
The preferred embodiment of the storage tank according to the present invention includes a plurality of arcuate wall panels, each formed of a plurality of superimposed precast concrete panel sections, joined end to end by vertically extending pilasters to form a cylindrical tank wall. The tank is versatile due to the modular construction thereof; i.e., the height of the tank wall is determined by the number of superimposed panel sections which are utilized. For example, if a fifteen foot high tank is desired, the wall may be constructed of panels comprised of three superimposed panel sections, each section of five foot height. Further, if it is subsequently desired to increase the capacity of the tank by increasing the height of the tank wall to, for example, twenty feet, this can be achieved by the simple addition of one five footh high section to each wall panel. The tank wall is supported in a novel fashion by a plurality of circumferently spaced concrete footings located beneath each vertical pilaster. The footings are formed separate from the tank floor but are interconnected through radially directed spokes to facilitate the capability of the tank to withstand a greater degree of seismic loading than was heretofore known. The tank floor may be formed from a poured-in-place concrete slab after construction of the tank wall, eliminating the need for the construction of a circular form, or the floor may be fabricated at least in part from precast concrete elements.
The cylindrical wall of the tank if prestressed in anticipation of the forces generated by the material to be stored by the provision of vertically spaced wires or tendons tensioned around the tank periphery. The vertical spacing of the tendons is varied according to the computed force load along the vertical extent of the wall and the tendons are secured to two diametrically opposite stressing pilasters. The possibility of progressive failure of the tank due to implosion forces in the event that a single panel section should fail is negated by the fact that the pilasters are post-tensioned vertically and capable of resisting implosion due to a sudden emptying of the tank due to failure of one of the sections. If such an event should occur the tank will be repairable rather than totally demolished.
It is therefore the primary object of the invention to provide a storage tank having a novel modular construction which is versatile in utilization, structurally sound, and is facile and economical in fabrication and relocation.